Kotlin coroutines don't really exist. They're a (very neat) programming trick to support coroutine-like behavior on the JVM which doesn't support coroutines. If you look at the bytecode it produces, it honestly is a mess. And it colours your functions too: now you have be ever careful that if your function is running in a coroutine, there are certain things you should absolutely avoid doing in that function, or any function called by that function (like spinning the CPU on loop without yielding). In Go, you don't have to worry about any of this because the concurrency is built-in from the start.

Also I don't understand "it's not trivial to grow them". It is trivial to grow them, and that's why Go went this way. Maybe only 0.1% or fewer of use-cases will ever find any issues with the resizing stack (in fact probably the majority of uses are fine within the default starting stack size).